1. Field of the Invention
The present invention relates to a device for separating and extracting components having different densities from an effluent and more particularly to a device for service in oil wells for the purpose of separating water from the crude oil constituting the major part of the effluent which penetrates into a wellbore.
2. Description of the Prior Art
Gas and/or oil wells extend through formations in which one or a number of productive formations contain not only oil or gas but also substantial quantities of undesirable products such as water (usually salt water). Such products are present in large quantities which may attain 90% of the effluent, especially towards the end of the productive life of a pay formation.
A number of different methods have been adopted for separating and extracting oil and/or gas from salt water.
A first method consists in extracting the entire quantity of effluent from the wellbore and separating the components at the ground surface by various means such as the gravity settling process. In this process, the oil and/or gas is recovered whilst the salt water is reinjected into a reinjection zone, in most cases through another wellbore.
A process of this type has been abandoned for economic reasons and also for technical reasons, due consideration being given to the energies which have to be produced in order to displace the effluent from the pay formation up to the surface prior to separation of oil and/or gas from the salt water.
A second known process consists in separating the oil and/or gas from the water beneath the ground surface so as to ensure that the oil alone is lifted to the surface, the water being reinjected into a formation around the wellbore and usually into a formation located above or below the productive horizon to be developed.
U.S. Pat. Nos. 4,241,787 and 4,296,810 relate to a process for extracting oil from a fluid effluent which contains both oil and water. This process consists in bringing the effluent from the formation into a separator located within the wellbore, in passing the effluent through a filter which is permeable to one of the components and placed within said separator, in maintaining a pressure gradient across the filter, then in pumping the separated oil on one side of the filter and in pumping the water on the other side of said filter in order to feed said water back into a reinjection zone.
The device for carrying out the process outlined in the foregoing includes two pumps mounted in parallel and driven from a single electric motor, pressurization of the effluent being carried out in response to the pressure developed within the formation and to the sucking action produced by all the pump sets through the separator.
However, these methods and devices entail the need to make use of a pump for each component of the effluent and also call for the use of a separator having a relatively complicated structure. The effluent is in fact required to pass through a first filtering material in order to remove solid particles such as grains of sand, for example, then through semipermeable membranes adapted to each component of the effluent. By reason of the specificity of membranes, however, it is preferable to employ a plurality of membranes for each component in order to guard against tearing of membranes under the action of the high pressures involved. The energy developed by the pumps must not only be of high value in order to overcome the resistance of the separator filters but must also be sufficient to lift the extracted oil to the surface and to discharge the salt water into the selected reinjection zone. Moreover, when the reinjection energy is too high, it is a recommended practice in such a case to lift the salt water also to the ground surface. Needless to say, this shows the limitations of such a device. Finally, it is not an easy matter to remedy any operational fault conditions which might arise in one of the pumps and more particularly the pump located at the lowest level since it is first necessary to lift the upper pump to the surface.
In the case of another known device as described in U.S. Pat. No. 3,167,125, separation of the effluent components is performed by gravity within the wellbore. Extraction of the heaviest component takes place through a sucker-rod pump which is capable of sucking said heavy component and of discharging it into a selected reinjection zone. The lighter component is displaced up to the surface solely under the action of the pressure existing within the producing formation. However, when the formation pressure is insufficient, it is necessary in such a case to make use of another pump for extracting said light component.